A conventional rotary looptaker of the type described above is disclosed in Japanese Utility Model No. 57-13024. A looptaker body is provided with a raceway having an upper flat surface. A bobbin case has a flange with a flat lower surface which is engageable with the upper surface. When a sewing machine is driven, the looptaker body is rotated relative to the bobbin case with sliding contact through both flat surfaces.
In such a conventional looptaker, however, the looptaker body and the bobbin case are in engagement with each other through the relatively large contact area between the flat surfaces, so that sliding friction between the flat surfaces is large and a large rotative force is imparted to the bobbin case owing to the large sliding friction when the looptaker body is rotated relative to the bobbin case. Consequently, excessive noise and vibration are produced because of that friction when the bobbin case is restrained from rotary motion in the presence of the large rotative force. The noise and vibration are generated by the contact of a restraining projection on the bobbin case with a restraint element secured to the machine frame.